42 CFR 423.346 - Reopening.
(a) CMS may reopen and revise an initial or reconsidered final payment determination (including a determination on the final amount of direct subsidy described in § 423.329(a)(1), final reinsurance payments described in § 423.329(c), the final amount of the low income subsidy described in § 423.329(d), or final risk corridor payments as described in § 423.336) or the Coverage Gap Discount Reconciliation (as described at § 423.2320(b)) -
(1) For any reason, within 12 months from the date of the notice of the final determination to the Part D sponsor
(2) After that 12-month period, but within 4 years after the date of the notice of the initial or reconsidered determination to the Part D sponsor, upon establishment of good cause for reopening; or
(3) At any time, in instances of fraud or similar fault of the Part D sponsor or any subcontractor of the Part D sponsor.
(b) For purposes of this section, CMS will find good cause if -
(1) New and material evidence that was not readily available at the time the final determination was made is furnished;
(2) A clerical error in the computation of payments was made; or
(3) The evidence that was considered in making the determination clearly shows on its face that an error was made.
(c) For purposes of this section, CMS will not find good cause if the only reason for reopening is a change of legal interpretation or administrative ruling upon which the final determination was made.
(d) A decision not to reopen under this section is final and is not subject to review.